The Caspian Sea is the largest enclosed body of water on Earth by area, variously classed as the world's largest lake or a full-fledged sea. The sea has a surface area of 371,000 km2 and a volume of 78,200 km3. It is in an endorheic basin (it has no outflows) and is bounded to the north by Russia, to the south by Iran, western Azerbaijan, and eastern Kazakhstan and Turkmenistan. (View Larger Map)

Abdolreza Karbasi, of the deputy marine branch of the Iran Environmental Organization, said on Wednesday: "The Republic of Azerbaijan carries out its petroleum activities with worn-out devices and it is not concerned about its capacity to clean this body of water."

The report indicates that a recent investigation of the coastal region of Gilan province in northern Iran has shown that a growing number of oil blotches are visible in the waters.

Karbasi added that an estimate of clean-up costs will be prepared, and the Iranian Foreign Ministry will present it to Azerbaijan as a fine.

An earlier report had indicated that satellite pictures revealed oil blotches as large as 110 km across floating toward Iran from the Azerbaijan Republic.